Material handling mechanism



June 12, 1956 H. HARDINGE 2,750,038

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MATERIAL HANDLING MECHANISM Filed Aug. 23, 1951 8 Sheets-Sheet 3 INVENTOR. HQEL 0w: mqew/ma' 8 Sheets-Sheet 4 Filed Aug. 25, 1951 INVENTOR. HfiLOA/Z' #460/0'65 June 12, 1956 H. HARDlNGE MATERIAL HANDLING MECHANISM 8 Sheets-Sheet 5 Filed Aug. 23, 1951 E] III INVENTOR. HQELOA/l fiGD/HGZ' June 12, 1956 H. HARDINGE 2,750,038

MATERIAL HANDLING MECHANISM Filed Aug. 23, 1951 I 8 Sheets-Sheet 6 June 12, 1956 H. HARDINGE MATERIAL HANDLING MECHANISM Filed Aug. 23; 1951 8 Sheets-Sheet 7 m J KUmIU omu JOEPZOU OZI HHONIIAI) ,q TraK/ June 12, 1956 H. HARDINGE MATERIAL HANDLING MECHANISM 8 Sheets-Sheet 8 Filed Aug. 25, 1951 MATERIAL HANDLING MECHANISM Harlowe Hardinge, York, Pa.

Application August 23, 1951, Serial No. 243,328

21 Claims. c1. 210-55 This invention relates to material handling mechanisms such as thickeners, clarifiers, hydro-classifiers, large agitators and the like and a method of operating the same. Mechanisms of this type comprise some form of tank in which a central, substantially vertical drive or torque shaft is mounted for rotation about its axis and material engaging means within the tank are rotatably moved by said shaft. In general, said shaft and the material en gaging means actuated thereby rotates quite slowly and the shaft is subjected to relatively high torque. More particularly, the present invention relates to mechanisms and methods of operating the same for rotatably driving said shaft in material handling mechanism of this nature as well as for elevating said shaft and the material en gaging means thereon upon the latter encountering an obstruction during the operation thereof.

In such mechanisms, fluid containing particles or solids or" various sizes are introduced into the tank and the principal purpose of the mechanism is usually to remove certain of said particles or solids or substantially all of the same from the fluid which contains them when introduced into the tank. Such operation may be performed, for example, by permitting the particles and solids to settle to the bottom of the tank and the material engaging means of the mechanism usually comprises scrapers of one form or another, all well known in the art, said scrapers being slowly rotated by the torque shaft of the mechanism so as gradually to collect the settled sediment or sludge adjacent the bottom of the tank and move the same to an outlet provided therefor in accordance with customary practice. The relatively clear or clean liquid from which the particles have been re moved flows from the upper portion of the-tank. Inasmuch as it is not uncommon for some of the tanks in mechanisms of this type to be as much as 100 feet or more in diameter, and since the scraper arms of the material engaging means extend either radially from the center or diametrically across approximately the entire width of the tank, it is obvious that high torques are imposed upon the central drive or torque shaft which rotates the material engaging means.

In order that the settling function occurring within the tank will not be disturbed any more than necessary during the operation of the mechanism, the material engaging means usually is moved relatively slowly. Thus, for example, the peripheral speed of the ends of the scraper arms usually is within the range of from 12 to 15' per minute but it is to be understood that this may be varied for specific purposes. As the diameter of the tank and the corresponding length of the scraper arm is increased, the speed of the drive or torque shaft decreases in order to achieve the desired peripheral speed of the ends of the scraper arms. Correspondingly, the larger the diameter of the tank, the greater the torque imposed upon the drive or torque shaft. For purposes of simplifying terminology herein, the drive or torque shaft by which the material engaging means is driven is referred to here- States Patent Patented June 12, 1956 inafter generically as a torque shaft but it is to be understood that said generic term embraces all types of members whether solid or tubular, a frame-work or combination thereof, used to drive the material engaging means of the type to which this invention pertains.

Heretofore, various kinds of large and usually expensive gear trains have been utilized in order to drive the torque shaft and an economical type of gear train has not been possible up to the present time, especially in the larger sizes of tanks in these mechanisms, because of the foregoing factors and particularly the slow speed and high torque to which the torque shaft is subjected to produce the desired results by the material engaging means. Further, high power input has been required to drive such relatively inefiicient gear trains and this has of course added to the cost of operation of the mechanism.

It is the principal object of the present invention to obviate the use of a gear train as such to drive the torque shaft in mechanisms of this nature by utilizing a simple and economically operable drive mechanism and method embodying the principle of converting reciprocating motion to rotary motion.

Another object is to provide in the preferred embodiment of the invention hydraulic means to produce reciprocating motion in the drive mechanism, whereby almost unlimited force may be generated by said hydraulic means which requires relatively low power input and is capable of driving the torque shaft of mechanisms of this nature of any practically feasible size.

Still another object of the invention is to provide driving means for said torque shaft which is operable not only to convert reciprocating motion to rotary motion but convert it in such a manner that the rotary motion is substantially continuous and uni-directional.

A further object of the invention is to provide a number of preferred embodiments of ratchet wheel and driving pawl systems by which said reciprocating motion is converted to substantially continuous and uni-directional rotary motion.

As a corollary to the preceding object, one of said embodiments of ratchet and pawl systems utilizes a push-pull type of pawl assembly and several other embodiments utilize a plurality of similar pawls, integrated during their operation to as sequentially to engage the ratchet wheel in driving relationship, all said embodiments of ratchet wheel and pawl systems functioning however to drive said ratchet wheel substantially continuously and uni-directionally.

It is still another object of the invention to provide the first mentioned embodiment of the foregoing corollary with teeth on the ratchet wheel having cam shaped driving faces engageable by the pawls in a manner to effect continued rotation of the ratchet wheel while the pawls are being moved radially into the notches between the teeth of the wheel; and arrange the several other embodiments mentioned in said corollary so that there is an overlapping of the driving movements of the pawls; whereby all embodiments function to produce actual continuous and uni-directional rotation of the ratchet wheel as well as of the torque shaft and material engaging means driven thereby.

A still further object of the invention is to include in the mechanism of the various embodiments uniquely operated means for elevating the torque shaft and material engaging means in the event the latter encounters an obstruction such as an unusual settling or precipitation of sediment within the tank so that an overload is imposed upon the torque shaft and the driving means therefor.

Incident to the foregoing object, the preferred embodiment of elevating means is hydraulically operated by fluid from the source which supplies the motivating force for the drive means for the torque shaft, said mechanism also including pressure actuated control means operable to cause the elevating means to be actuated upon the overload resistance imposed upon the torque shaft and driving means reaching a pre-determined pressure, whereupon the elevating means will function to raise the torque shaft and material engaging means within the tank so as to overcome or be relieved from some or all of the obstruction or overload condition and thereafter permit the drive means to resume its normal rotation of the torque shaft and sediment engaging means.

Details of the foregoing objects and of the invention as well as the objects thereof are set forth in the following specification and illustrated in the accompanying drawings forming a part thereof.

In the drawings:

Fig. l is a top plan view of an exemplary material handling mechanism including one embodiment of driving mechanism embodying the principles of the present invention, part of said figure being broken away.

Fig. 2 is a side elevation, partly in transverse section, illustrating the exemplary material handling mechanism shown in Fig. l and the embodiment of driving mechanism also shown in Fig. 1.

Fig. 3 is an enlarged top plan view of the driving mechanism illustrated in Figs. 1 and 2.

Fig. 4 is a sectional side elevation of the driving mechanism illustrated in Fig. 3 and taken on the line 44 thereof.

Figs. 5, 6 and 7 are respectively enlarged diagrammatic layouts illustrating progressive steps during the operation of the embodiment of driving mechanism illustrated in Figs. 1 through 4.

Fig. 8 is an enlarged diagramatic view showing fragmentary details of a variation of one of the pawls of the driving mechanism illustrated in Figs. 1 through 7.

Fig. 9 is an enlarged side elevation of the driving mechanism illustrated in Figs. 1 and 2 and also illustrating elevating means for raising the torque shaft.

Fig. 10 is a top plan view illustrating another embodiment of driving mechanism for the torque shaft of the exemplary material handling mechanism shown in Figs. 1 and 2.

Figs. 11, 12, and 13 are diagrammatic layouts illustrating progressive steps in the function of the embodiment of the driving mechanism illustrated in Fig. 8, said figure being on a larger scale than that used in Fig. 8.

Fig. 14 is a plan view of still another embodiment of driving mechanism for the torque shaft of the exemplary material handling mechanism shown in Figs. 1 and 2.

Fig. 15 is a schematic diagram of the hydraulic system employed in the embodiment illustrated in Figs. 14 and 16.

Fig. 16 is a side elevation of the embodiment of the invention shown in Fig. 14.

Referring to the drawings, and particularly Figs. 1 and 2, an exemplary material handling mechanism illustrated therein comprises a tank 10 having a bottom 12 and a superstructure 14 supported by the top of the tank. Said superstructure supports the driving mechanism 16 and elevating mechanism 18, details of which are set forth hereinafter. Fluid containing entrained particles and solids to be treated is supplied to the tank in accordance with conventional practice by a feeder launder 20. The exemplary mechanism shown herein is a thickener but, as stated hereinabove, the principles of the invention are equally applicable to other types of material handling mechanisms of the class specifically mentioned hereinabove as well as other similar mechanisms.

Liquid containing solids is introduced through the launder 20 which fills the tank to the upper edge of the overflow wier 22 and over which the liquid flows and is discharged through port 24. Particles of various sizes which have settled from the inflowing liquid accumulate on the bottom as a relatively dense mass 26.

Referring to Figs. 3 and 4, a ratchet wheel 30, comprising part of the drive mechanism of one embodiment of the present invention, is rotatably supported by a bearing assembly 32, the ratchet wheel also being fixed to the upper end of and supporting a depending, substantially vertical torque shaft 34 which, in the exemplary embodiment, is illustrated as a tube. The bearing frame 36 is fixed to the superstructure 14 for support and the torque shaft, which may comprise a plurality of interconnected sections, is disposed substantially centrally of the tank 10 as shown in Fig. 2. Material or sediment engaging means 38 comprising in this particular illustration a cross-arm 40 and a plurality of spiral scrapers 42 fixed thereto and rotated thereby, engage sediment material settled upon the upper surface 28 of the mass 26 and, upon the scrapers 42 being slowly rotated by the torque shaft 34, the accumulated sediment is moved relative to the surface 28 to a central discharge port 44. All of the foregoing description of operation is in accordance with customary practice.

It will be seen from the foregoing description of the mechanism illustrated herein that, particularly if the diameter of the tank 10 is great, a very substantial torque is imposed upon the torque shaft 34 while moving sediment engaging means 38 which are directly connected to the lower end of torque shaft 34. Even though the speed of rotation of the sediment engaging means is relatively slow and the peripheral speed thereof is, for example, of the order of 12 to 15' per minute, it is nevertheless preferred to have the motion as continuously even as possible. However, even if the motion were not continuous, this would not necessarily detract from the efficiency of the scraping function of the material engaging means of the exemplary thickener mechanism shown herein because the overall speed is very low.

It has been noted in many cases that, during the operation of the scraper blades when driven by a conventional gear train, the actual movement of the scraper blades varies due to the material engaging means encountering resistance within the tank. Under such conditions, the action of the scraper blades is usually more or less intermittent. The driving torque developed by the driving means for the mechanism increases to a point where the scraper blades start to move across the surface 28 and such movement will continue until resistance is built up to such an extent that the scraper blades will stop momentarily until the torque force of the drivin mechanism is again built up so as to cause the blades to commence moving again and thus the motion of the scraper blades is somewhat a succession of starts and stops even though the gear train driving the blades is moving at a constant speed. However, regardless of this condition which sometimes exists, it is advantageous to endeavor to maintain the rotary motion of the mechanisms substantially continuous, such as where classification between one size and another of particles is desired, such devices being known in the art as a hydro-classifier or hydro-separator.

As has been stated above, driving mechanisms for the torque shafts of devices of this nature have embodied gear trains to develop the necessary driving torque to move thematerial engaging means attached to the torque shaft and driven thereby. Relatively large power input is required to actuate said gear trains in order to achieve the desired rotation of the material engaging means within a tank.

Unlike the gear train type of driving mechanisms, the present invention provides a number of embodiments of driving mechanism utilizing a method and means of converting reciprocating motion to rotary motion. Reciproeating motion may be generated relatively inexpensively 5 by simple mechanism such as a pump which furnishes fluid under pressure to a hydraulic cylinder for driving a piston therein in opposite directions. The reciprocating motion may, however, be provided by means utilizing force's other than hydraulic pressure and the present invention, in its broader aspects, is not to be restricted to the use of hydraulic pressure forces for developing the reciprocating motion embodied in the herein illustrated and described driving mechanism.

One preferred embodiment of driving mechanism employing the principles of the present invention is illustrated in Figs. 1 through 4 in which a hydraulic cylinder 46 is supported by part of the superstructure 14. Said part, for example, may be a flat plate 48 to which an anchor bracket 50 and a plurality of guide bearings 52 are secured. One end of the cylinder 46 is pivotally secured to the bracket 50 by a pin 54 or any other similar means and a piston rod 56 is reciprocable by a piston within the cylinder 46. A reciprocating rod 58 is flexibly connected to the piston rod 56 such as by a pivot pin 60, whereby the cylinder 46 and piston rod 56 have a certain amount of self-aligning ability to prevent binding during operation thereof.

A hydraulic pump 62 is also fixed to the plate 48 and is driven by motor 64, likewise fixed thereto. Pressure supply line 66 and return line 68 are connected between the pump and a control valve 70. Fluid lines 72 and 74 are respectively connected between opposite ends of the cylinder 46 and the control valve 70. While the present invention is not restricted thereto, the valve 70 is preferably of the solenoid actuated type and of standard construction; thus details thereof are not illustrated herein. Said valve is arranged to be actuated by a plurality of switches 76 and 73 which are, in turn, actuated by means to be described.

Control valve 70 is of the type that, when set in one position, the pump 62 will supply fluid under pressure to one end of the cylinder 46 and, when the valve is set in another position, the pump will supply fluid to the other end of cylinder 46, whereby the piston rod 56 and reciprocating rod 58 are moved in opposite directions by the piston within the cylinder 46.

The switches 76 and 78 are also preferably of the snapacting type which function when the operating arms 108 thereof are moved a predetermined amount and a conventional spring, not shown, or other suitable means, then returns the arm to starting position, when the arms have been cleared by detents 106 moving past the same, and incidentally reverse the switch. By the time the arm is returned however and the switch is reversed, the valve 78 has been shifted and will remain so shifted until further actuated by the switch other than that which last shifted the valve.

Fixed to the reciprocating rod 58 intermediately of the guide bearings 52 is a yoke 80 reciprocable with said rod. A plurality of pawl carrying arms 82 and 84 are pivotally connected at one end to the yoke 80 as clearly shown in Fig. 3. Heads 86 are longitudinally adjustably connected to the arms 82 and 84, said heads thus comprising parts of said arms and respectively carrying pawls 88 and 99. It will be noted that the pawl 88 is arranged to engage the ratchet Wheel teeth in a pulling relationship and pawl 90 is arranged for such engagement in a pushing relationship. The heads 86 also carry depending rollers or pins 92 and 94 for purposes to be described.

In the push-pull pawl embodiment of drive mechanism illustrated in Figs. 3 and 4, the teeth of the ratchet wheel 30 comprise two integrated sets of slightly differently shaped teeth in order to provide optimum efiiciency in engagement between the pawls and the ratchet Wheel teeth during the sequential driving movements of the pawls and not have to resort to compromise on a single tooth form engageable by both the pushing and pulling pawls.

Specifically, the working faces of the ratchet wheel teeth which are engaged by the pawls 88 and are each preferably two angularly related surfaces in order to insure maximum efficiency in driving engagement by the pawls. This is best shown in Figs. 5 through 8. Such arrangement insures, for example, against the pawls tending to slip radially outward from engagement with the working faces of the ratchet wheel during the angular displacement of the ratchet wheel while being driven by the pawls. Moreover, the inclination of the working faces of all the ratchet wheel teeth of one set relative to the radius of the wheel is different from the inclination of the working faces of all of the teeth of the other set relative to the radius of the wheel. Thus, the best angle of action for the sets of ratchet wheel teeth which respectively are pushed and pulled by the pawls 88 and 90 may be obtained by such use of said two integrated sets of differently shaped teeth.

Notwithstanding the foregoing arrangement of teeth, it is to be understood that a ratchet wheel may be used having a single set of teeth all having the same shape, said shape being such as to be operable with either the pull type pawl 88 or the push type pawl 90. In the latter instance, the peripheral length of each tooth and the movement of the rod 58 could be such that each reciprocation of the pawls by the rod 58 would rotate the ratchet wheel a distance amounting substantially only to the peripheral length of each tooth. However, in the specific embodiment illustrated in Figs. 3 and 4, the alternate disposition of pull type teeth 96 and push type teeth 98 requires each reciprocation of the pawls by the rod 58 to rotatably move the ratchet wheel a distance equivalent substantially to the peripheral length of two adjoining teeth 96 and 98.

The outer ends of the arms 82 and 84 and the pawls carried thereby are resiliently urged constantly radially in a direction to seat the pawls within the notches between the teeth of the ratchet wheel, said urging means in the preferred embodiment comprising a pair of spaced, parallel springs 100 connected at their ends to the arms 82 and 84 intermediately of the ends thereof as clearly shown in Fig. 3.

In Fig. 3, the illustration is such that the ratchet wheel is being rotated clockwise as indicated by the arrow, the rod 58 is moving toward the cylinder 46 as also shown by the arrow, and the pulling pawl 88 is in engagement with one of the teeth 96 and is moving in driving direction. Meanwhile, pushing pawl 90 and the arm 84 are moving in non-driving direction.

In order particuiarly to minimize wear between the pawls and the teeth of the ratchet wheel, the pawls 88 and 9 are prevented from dropping into the working notch of the tooth intervening the teeth of the set engaged sequentially thereby by means carried by the ratchet wheel and comprising segmental, arcuate lugs 182 space even distances apart and projecting upward from the web of the ratchet wheel as shown in Figs. 3 and 4. There are only half as many lu s 182 as there are teeth the ratchet wheel and said lugs are engaged by the pins 92 or 84 of the arms 82 or 84 during a portion of the movement of said pins and arms in noti-driving direction. Thus, referring to Fig. 3, it will be seen that the pin 92 is in engagement with the outer arcuate surface of one of the lugs 1&2 and the position of the lug 162 relative to the pushing pawl 9i? is such that said pawl is prevented from dropping into the notch 184 even though the springs 100 are endeavoring to move the pawl into said notch. The length of each lug 102 is such that when, for example, the pin 94 clears the trailing end of the lug, the working face of the tooth to be engaged by the pawl is substantially opposite the working face of the pawl and the springs 15!) will move the pawl radially into engage ment with the working face of the tooth which is to be driven by said pawl.

Referring still to Fig. 3, the pulling pawl 88 will continue to rotate the ratchet wheel by moving in driving cal-sepsis direction until the pin 94 has cleared the trailing end of the lug 102 presently holding the pushing pawl 90 out of the notch 104 and, when this occurs as aforesaid, the pushing pawl 9% will drop radially into engagement with the working face of the tooth 98 due to the tension of the springs ltltl. During such radial movement of the pawl 90, a deteut 106 or any other suitable means on the head 86 carrying the pawl 90 engages the operating arm 108 of switch '78 and instantaneously causes the valve '70 to shift so as to reverse the direction of oil pressure flow to cylinder 46 which immediately reverses the direction of reciprocation of the rod 58.

Such movement of the pushing pawl l is illustrated diagrammatically in enlarged scale in Fig. 7 wherein a segment of the lower portion of the ratchet wheel 30 is shown and an upper portion of said ratchet wheel is also shown adjacent said lower portion in order to illustrate such segments in enlarged scale in the relatively small space of a. standard size drawing. However, in Fig. 7 and also in Figs. and 6 the angular relationship between the pawls and the teeth of the ratchet wheel is the same as in smaller scale Fig. 3 in which the entire ratchet wheel is shown. Fig. 7 serves to show more clearly how the inward lateral movement of the pushing pawl 99 incidentally effects actuation of switch 78 as a result of the corresponding inward movement of the outer end of arm 84. The pushing pawl Ml, when fully in driving engagement with one of the teeth 98, as shown in Fig. 5, continues to rotate the ratchet wheel in its same rotary direction. Meanwhile, the arm 82 and pulling pawl 88 will now be moving in non-driving direction and the pawl 88 will be riding up the non-working face of the tooth 98 immediately to the left of the pawl as viewed in Fig. 7. This causes the outer end of arm 82 to move radially outward. carrying pin M therewith so as to he engageabie with the outer surface of the next presented lug 102, resulting during continued rotation of the ratchet wheel in the pulling pawl being held against radial movement into contact with the working face of the intervening tooth 93 between the teeth 96 which are successively engaged by said pulling pawl when moving in driving direction.

The pushing and pulling pawls actually travel a distance equal to the length of one tooth on the ratchet wheel. However, for example, while the pushing pawl is pushing the ratchet. wheel in driving direction a distance of one tooth, the pulling pawl is likewise moving a distance actually equal to the length of one tooth in non-driving direction but, due to the movement of the ratchet wheel during such movement of the pulling pawl, the pulling pawl will be moved relative to the ratchet wheel a distance of two teeth and then be in position to drop radially into operative engagement with the working face of the next presented tooth $6. as shown in Fig. 5. As shown in Fig. 3, the operating arm 103 of switch '76 will be en ed by detent 166 on the head 86 carrying the pulling p? $33 as a result of the latter chopping radially into engagement with said working face of the next tooth )6. The operation shown in Fig. 5 is the opposite of Fig. 7 in that. in Fig. 7, the pawl 94 is dropping into operable position whereas, in Fig. 5, the pawl 88 is dropping into operable position. Upon the pulling pawl 88 commencing its driving of the ratchet wheel 39, the pushing pawl will move in non-driving direction, climbing the non-working face of the adiacent tooth 5'6 of the ratchet wheel and thus moving radially outward to position the pin 9 on the arm 84 into position to engage the next presented lug 102. as shown in Fig. 6. and thereby holding pushing pawl 90 out of engagement with the notch intervening those into which it is intended to drop.

From the foregoing, it will be seen that the pushing and pulling type pawls successively and sequentially move in driving direction and engage teeth of the ratchet wheel so as to cooperate substantially continuously to rotate the ratchet wheel uni-directionally and correspondingly rotate and drive the torque shaft 34 and the material engaging means 38 actuated thereby. Such rotation is substantially continuous and the movement of the ratchet wheel and attached means is interrupted only for an instant as a result of the very short time required to reverse substantially instantaneously the reciprocating direction of rod 58 and the arms 82 and 84 connected thereto and effect radial movement of the pawls into driving engagement with the ratchet wheel so as to resume driving rotation thereof. As the mechanism wears, a certain amount of play will develop between the relatively moving parts thereof which will likewise result in momentary interruption of the rotation of the ratchet wheel while the rod 58 and the pawl mechanism actuated thereby is being shifted in its direction of reciprocation.

The type of valve 70 and the switches actuating the same are such that shifting of the valve is achieved as instantaneously as possible so as to minimize the interruption of the rotation of the ratchet wheel during the resulting shifting of the direction of reciprocation of the pawl mechanism. However, such momentary interruption of the rotation of the ratchet wheel does not unduly detract from or impair the resulting operation of the material engaging means because, as stated above. the rotation of the material engaging means itself is hardly ever actually continuous and free from at least momentary interruption due to the nature of the impedance imposed upon the material engaging means by the continuous engagement thereof with obstructions in the media within the tank and through which the material engaging means is moved.

One means within the purview of the present invention for achieving actual constant rotation of the ratchet Wheel and the material engaging means driven thereby comprises the formation of the working face of the teeth of. the ratchet wheel so as to be at a small angle to the radial direction of movement of the pawls While moving radially to said working face when the pawls are being moved into the notch adjacent the working face of each tooth engaged by the pawl. An enlarged illustration of such an arrangement is shown in Fig. 8 wherein the pulling pawl 88 has been selected to illustrate the operation described. In this figure, it will be seen that at least the outer face portion 11% of a teeth 96 is disposed at an angle A to the working face 112 of the outermost portion of the pawl 38. Said angle may vary according to required conditions in a specific mechanism but such angular disposition should be such that the inward radial movement of the pawl by the force of the springs will preferably cause rotary movement of the ratchet wheel at substantially the same rate of speed as that produced by the movement of the pawl when in full engagement with a tooth of the ratchet wheel while being moved in driving direction. It will be understood of course that the relationship between the working faces of the pushing pawl 90 and the ratchet wheel teeth 98 engaged thereby will also be similar to that illustrated in Fig. 8 and described hereinabove relative to the pulling pawl 88 and the ratchet wheel 96. By using ratchet wheel teeth formed as thus described and illustrated, actual continuous rotation of the ratchet wheel may be achieved.

Another embodiment of driving mechanism is illustrated in its entirety in Fig. It) and certain steps of the operation thereof are individually illustrated in a larger scale in Figs. ll, 12 and 13 as will be described hereinafter.

Referring to Fig. 10, the ratchet wheel 30 is provided with a series of similar teeth 114. These teeth are engaged by similar pawls 116 and 118 individually actuated by separate hydraulic cylinders 120 and 122. All of the driving mechanism of this embodiment may be supported on a suitable common means similar to plate 48 in the above described embodiment. Each of the cylinders 120 and 122 is provided with a separate pump 124 and 126, preferably actuated by a single motor 128. Fluid supply aromas lines clearly shown in Fig. connect the pumps with the cylinders and said supply lines also communicate with control valves 130 and 132 which are preferably solenoid actuated but may be mechanically actuated if desired. Said valves are similar to valve 70 of the above described embodiment and are of standard construction. The cylinder 120 reciprocates a piston rod 134 and cylinder 122 reciprocates a piston rod 136. Piston rod 134, in turn, actuates reciprocating rod 138 mounted in suitable guide bearings 14% and piston rod 136 actuates reciprocating rod 142 mounted in guide bearings 144.

Pivoted to the outer end of reciprocating rod 138 is an arm 146 carrying pawl 116, while reciprocating rod 142 has an arm 148 pivoted to the outer end thereof .and carries pawl 118. In this specific embodiment of the invention, the pawls 116 and 118 are illustrated as being of the pushing type but it is to be understood that they could equally well be of the pulling type and engage the teeth of the ratchet wheel 36 in pulling fashion merely by reversing the ratchet wheel on its shaft, for example. The outer ends of the arms 146 and 148 which carry the pawls 116 and 118 respectively are constantly urged radially into the notches between the teeth 114 of the ratchet wheel by springs 158 which may, for example, actuate pressing shoes 152 which directly engage the heads 154 adjustably connected to the outer ends of rods 146 and 148 and comprising a part thereof.

Unlike the above described embodiment in which only a single actuating switch is operated by each pawl carrying arm for controlling the shifting valve for the hydraulic cylinder, the present embodiment employs a pair of switches for each reciprocating means respectively actuating the pawls 116 and 118. As clearly shown in Fig. 10, a pair of switches 156 and 158 are positioned adjacent the line of movement of the reciprocating rod 138, these switches having actuating arms 160. The reciprocating rod 138 also has detents 162 and 164 mounted adjacent opposite ends thereof and engageable respectively with the operating arms 168 of the switches 156 and 158. Similarly, a pair of switches 166 and 168, and the operating arms 170 are positioned adjacent the line of movement of the reciprocating rod 142, said rod having detents 172 and 174 fixed thereto adjacent opposite ends thereof, said detents being engageable respectively with the operating arms 178 of switches 166 and 168.

The switches 156 and 158 are connected by a circuit to control valve 130 of the cylinder 120 and, upon actuation, shift the valve so as to reverse the flow of hydraulic fluid between the pump 124 and opposite ends of said cylinder. Likewise, the switches 166 and 168 are connected by a circuit to the control valve 132 of the cylinder 122 for a similar purpose.

The operation of this embodiment of the invention is as follows: Referring to Fig. 10 and the diagrammatic showing in Fig. 11, pawl 116 has just commenced its movement in driving direction as a result of detent 162 having actuated the arm 168 of switch 156 and caused valve 130 to shift to connect the pressure supply line of pump 124 with the rear end of cylinder 120. As with switches 76 and 78, all of the switches illustrated in the present embodiment are of the type which close upon the operating arm being actuated and said arm is spring controlled so as to restore the arm to its normal position and open the switch when the arm is disengaged from the detent which has just actuated it, as when the detent moves past the arm.

Pawl 116 will continue to drive the ratchet wheel in driving direction, counter-clockwise in the particular illustration shown as indicated by the arrow, until the detent 164 engages the operating arm 160 of switch 158 as shown in detail in Fig. 12. When this occurs, the valve 130 is shifted rapidly in reverse direction to that described above and causes the pressure line of the pump 124 to be connected to the forward end of cylinder 120 to cause the reciprocating direction of the rod 138 to reverse instantaneously. When the rod 138 is thus reversed, it moves in non-driving direction and carries the pawl 116 therewith. However, during such movement of pawl 116 in non-driving direction, the pawl 118 will be driving the ratchet wheel 30 substantially continuously and uni-directionally and, while the pawl 116 is moving in nondriving direction, it will ride up the inclined non-operating face of the next succeeding tooth 114 under resilient pressure from the shoe 152 engaging the head 154 which carries the pawl 116, until the operating face of the next tooth 114 is disposed radially opposite the pawl 116. The spring pressed shoe 152 will then instantaneously move the pawl 116 radially into driving relationship with said operating face of the tooth and dispose it as shown in Figs. 1 l and 12 relative to said tooth.

T he switches 166 and 168 are operated by the detents 172 and 174 affixed to rod 142 which reciprocates the pawl 118 in both driving and non-driving direction under the influence of the hydraulic cylinder 122. Such operation is similar to that of switches 156 and 158, etc. relative to rod 138. The pawl 118 will also be moved by the rod 142 in driving and non-driving directions relative to suecessive teeth of the ratchet wheel, similarly to pawl 116.

The movement of the pawls 116 and 118 is integrated in such a manner that the movement of the pawls in driving direction overlaps to a sufiicient extent that actual continuous and unidirectional rotation of the ratchet wheel 30 is achieved. This overlapping occurs as a result of the movement of the pawls in non-driving direction taking place more rapidly than the movement thereof in driving direction. Such change in speed may, for example, occur as a result of the different displacement at one end of each of the cylinders 120 and 122 than at the other. That is, the piston rods 134 iand 136 displace some of the volume in the cylinders through which the piston rods reciprocate. Inasmuch as the volume of fluid as supplied by the pumps to either end of the cylinders is the same when under the same pressure, it is obvious that the movement of the piston and piston rods into the cylinders will occur more rapidly than the movement thereof outwardly in driving direction. The change in speed may be increased, for example, by using larger diameter piston rods in order to elfect a greater displacement at the rod ends of the cylinders.

Thus, since the non-driving or return stroke of the pawls and the actuating rods occurs more rapidly than the driving stroke thereof, it is possible to commence the driving stroke of one pawl shortly prior to the end of the driving stroke of the other pawl, whereby both pawls are moving in driving direction for a short interval of their paths of movement and, by such operation, any backlash or play in the driving mechanism is taken up or absorbed as described below and will result in no interruption to the continuous uni-directional rotation of the ratchet wheel.

Referring to Fig. 11, the pawl 116 has started its driving stroke and has moved a short distance in driving direction and pawl 118 has just finished its driving stroke and is in process of being reversed to moving in nondriving direction as a result of detent 174 actuating the arm of valve shifting switch 168. However, the ratchet wheel 30 is being driven now by pawl 116.

Referring to Fig. 12, pawl 116 is now approaching the end of its driving stroke and is close to shifting the control valve to institute movement of pawl 116 in non-driving direction which will occur when detent 164 actuates switch 158. Meanwhile, however, pawl 118 has moved a short distance in driving direction. Since pawl 118 is under no pressure at this time, pump 126 operates at somewhat higher volume displacement than when under pressure, a condition well known to those skilled in the art of displacement pumping, and the rate of travel of pawl 118 is more rapid than that of pawl 116. Pawl 118 thus soon catches up to tooth 114 and the pressure required of pump 126 increases until the pressures against both pawls, 116 and 118, are equal. At this time the force is then divided between the two pumps, 124 and 126.

When, as shown in Fig. 13, pawl 116 recedes from engagement with tooth 114 by reversal of direction through actuation of switch 158 by detent 164, then the entire pressure is taken up by pawl 118 and pump 126. In this case the speed of the wheel 30 will be slightly less than when both pawls are in action due to the slight increase in slippage or reduction in displacement of the pumps when under maximum pressure.

The cycle is then repeated and thus continuous rotary motion of the ratchet wheel is maintained.

Still another embodiment of the invention for continuously rotating the material engaging means Within the tank is illustrated in Figs. 14 through 16. This embodiment is similar to the embodiment shown and illustrated in Figs. through 13 to the extent that the plurality of cylinders 120 and 122 are used to actuate the piston rods 134 and 136 whinch in turn have heads 154 pivotally connected thereto. Said heads respectively have similar pawls 204 and 206 fixed to the outer end thereof. In the preferred arrangement of this embodiment, the pawls are the pulling type but it is to be understood that the same may be the pushing type similar to pawls 116 and 113 in said above described embodiment if desired.

This embodiment differs however from the embodiment of Figs. 10 through 13 in that only a single hydraulic 0 tinuous and uni-directional rotation of the ratchet wheel.

However, the means for achieving this is somewhat different from the aforementioned embodiment.

Referring to Figs. 14 and 15 and the schematic diagram of Fig. 16, it will be seen that the pressure line 210 from the pump 203 communicates directly with solenoid actuated valves 130 and 132 which are the same type in both embodiments. Fluid return line 212 is likewise connected to both of the valves 130 and 132 and the pump 200. Pressure lines 214 and 216 are respectively connected between valves 130 and 132 and the driving or piston rod end of each of the cylinders 120 and 122. Pressure lines 218 and 220 are respectively connected between the valves 130 and 132 and the non-driving or return ends of the cylinders 120 and 122 as is clearly shown in Figs. 14 through 16.

The pressure lines 214, 216, 218 and 220 all have adjustable flow control valves 222, 224, 226 and 228 con nccted therein between the valves 130 and 132 and the cylinders 120 and 122. These flow control valves may be of any type of a number of standard commercial valves that permit a controlled flow of fluid in one direction such as when the fluid is driving the piston but, when the fluid is returning to the Well of the pump 208, the flow is relatively unrestricted. The direction of the restricted or controlled fiow of the valves 222, 224, 226 and 223 is in the direction from the valves 130 and 132 to the cylinders 120 and 122.

In order that the movement of the pawls in nontlriving direction may be greater than in driving direction, so as to effect partial overlapping of the driving movements thereof, the flow control valves 226 and 228 are set to permit a greater controlled flow than the flow control valves 222 and 224 since the latter control the driving movements of the pawls and the former the nondriving or return movements thereof. Further, inasmuch as the cylinder 122 and its solenoid actuated control valve 132 are nearer the pump 208 than the cylinder and its valve 130, the frictional losses occurring in the feed line 230 between the valves and 132 would normally cause the cylinder 120 to receive less pressure than the cylinder 122 with a consequent slower movement of the pawl 204 than the pawl 206. To overcome such difference, the flow control valves 222 and 226 are set respectively to have a slightly greater flow in piston moving direction than the flow control valves 224 and 228, thereby overcoming the line friction referred to and causing the pawls 204 and 208 to reciprocate at the same driving speeds and also in the same non-driving speeds.

The reversal of movement of the pistons which drive the pawls 204 and 206 is effected by means of two pairs of switches 232 and 234 positioned respectively adjacent the two heads 154, the switches having operating arms thereon similar to the switches 156, 158, 166 and 168 of the above described embodiment, said arms being actuated by detents 240 and 242 on heads 154. Said detents preferably depend from the heads 154 as shown in Fig. 16, the switches 232 and 234 also being below the heads 154 as shown in Fig. 16, for purposes to be described.

For purposes such as to minimize wear on the pawls and the teeth of the ratchet wheel, as well as to give greater movement tothe pawls and thereby facilitate the partial overlapping of the driving stroke thereof, the arrangement and positions of the control means comprising the valves 232 and 234 as Well as the detents 240 and 242 is such that the pawls drivingly engage only alternate teeth of the ratchet wheel notwithstanding the fact that the teeth of the wheel are all similar as distinguishing from the teeth of the Wheel described in detail above relative to Figs. 3 and 4. There are, in effect, two sets of alternately interspersed teeth on the ratchet wheel 30 and pawl 204 will engage the teeth of one set while pawl 206 engages the teeth of the other set. Unlike the embodiment of Figs. 1 through 4, there is no need in the embodiment of Figs. 14 through 16 to hold one pawl out of engagement with the teeth intervening the alternate teeth to be engaged by said pawl when moving in driving direction. The positions of the switches 232 and 234 and their actuating arms below the heads 154 and the paths of movement of the detents 240 and 242 is such that the pawls will slidably move in non-driving direction from the tooth last engaged thereby, past the next tooth, and then move into the notch of the next succeeding tooth so as to be in position to drive it. Upon one of the pawls moving or dropping into said notch of said next succeeding tooth, the control arm of the switch 234 will be engaged by the detent 240 or 242, depending upon which pawl is being so moved, and thereupon shift the solenoid actuated valve 130 or 132 so as to reverse the direction of movement of the pawl from non-driving to driving direction.

Referring specifically to Fig. 14, the pawl 206 has just completed its driving stroke and is starting its movement in non-driving direction as indicated by the arrow on its head 1S4. Meanwhile, pawl 204 has overlapped the driving movement of pawl 206 and has been moving in the direction of the arrow on its head 154 for a short angle of movement of the wheel 30. Paw] 204 will con tinue to move in driving direction to rotate the wheel 30 as shown by the arrow and, meanwhile, pawl 206 will continue to move in its non-driving direction as shown by its arrow but at a more rapid rate than the pawl 204 is moving as a result of the greater hydraulic flow through control valves 226 and 228 than through valves 222 and 224. The pawl 206 will slide past the surfaces of the next tooth shown to the left thereof in Fig. 14, drop into the notch thereof and then slide over the inclined face of the second tooth to the left of the tooth now engaged by said pawl in said figure, dropping into the notch thereof and in so doing the detent 242 will move in engagement with the actuating arm of switch 234 and thereby cause a reversal of movement of the pawl 206 to driving direction. The aforementioned dropping of the pawl 286 into the notch of the next tooth to the left of the one engaged thereby in Fig. 14 will not actuate switch 234 because the detent 242 will merely move into the space between the switches 232 and 234 which control pawl 205. Further, due to the more rapid movement of pawl 206 in non-driving direction than in driving direction, the engagemet of pawl 266 with the second tooth to the left of the one engaged as illustrated in Fig. 14 will take place before pawl 204 has moved its entire driving distance and the detent 240 has engaged switch 232 which controls the end of the driving movement of pawl 204. This partial overlapping of the driving cycles of the pawls enables the pawl starting its driving cycle to catch up with the other pawl and be under full driving load before the latter pawl completes its driving cycle.

In view of the difference in pressures of the pawls moving in driving direction under full load and under either free or only partial loads as during the start of driving movement, a rapid take-up is achieved by each of the pawls when first starting their driving movement and not under load pressure or until they make contact and apply pressure against the ratchet wheel. The pawls thus rapidly are brought under full load, this occurring about the time that the detent on head 154 of the other pawl reaches its switch 232 so as to actuate the valve 130 or 132 and thereby shift the movement of the pawl completing its driving cycle to non-driving direction. Incidentally, the actual movements of the pawls relative to the ratchet wheel is the same as that described above relative to the embodiment of Figs. 1 through 7.

The mounting of the cylinders 120 and 122 is different in this embodiment from that in the embodiment of Figs. 10 through 13 in that no fixed guide bearings are provided for the piston rods 134 and 136. The fixed brackets i) are connected to one end of the cylinders by a pivot pin and the heads 154 are connected to the piston rods 134 and 136 by pivot pins 244. The guide bearing and stufiing box on each of the cylinders for the piston rods will serve to provide a certain amount of alignment between the head 154 and the cylinders. However, to maintain Working positions of the cylinders, piston rods, and heads, a plurality of adjustable stops 246, as shown in Fig. 14, are provided for purposes of limiting the pivotal movement of the cylinders. Tension springs 248 or other suitable urging means are connected between any suitable fixed points such as the valves 130 and 132 and an intermediate position between the ends of the head 154 for purposes of constantly urging the pawls into engagement with the teeth of the ratchet wheel and also into the notches therebetween.

In the above described embodiments of ratchet and pawl driving systems, the design of the driving mechanism is such that close tolerances need not be employed, yet substantially all unnecessary over-travel of the pawls and back-lash or interrupted motion is eliminated.

From the foregoing it will therefore be seen that a number of embodiments of efficient driving means are provided for performing a method of operating a material engaging means and the torque shaft actuating the same in material handling mechanisms of the type referred to heneinabove. The method and the embodiments of mechanism illustrated and described herein for performing it are based upon the principle of converting reciprocating motion to rotary motion and, while not restricted thereto, the preferred embodiment of the invention utilizes hydraulic means to provide the reciprocating motion. By using a pump to place fluid under pressure in the hydraulic cylinder of the several embodiments, a relatively small 14 powered motor may be used to drive the pump which, in turn, builds up pressure within the hydraulic cylinders until they actuate the reciprocating means for driving the pawls which cooperate with a ratchet wheel to convert the reciprocating motion to rotary motion. Regardless of the resistance offered by the material engaging means of the material handling mechanism, at least within reasonable limits, the pump or pumps of the several embodiments will continue to build up pressure in the hydraulic cylinders until the material handling means is moved. Thus, the present invention provides driving means which may be operated eifectively to drive a material engaging means at relatively slow speeds while subjected to very high torque and the small amount of power input required results in the driving means being operable far more economically than presently or previously used driving means in similar mechanisms.

In practically any material handling mechanism of the type to which the present invention pertains, the material engaging means occasionally encounters obstructions or abnormal resistance, the same being, for example, in the form of an unusual amount of solids in the fluid being treated, whereby an overload is imposed on the material engaging means and in turn upon the torque shaft and the driving mechanism therefor. Under these conditions, it is preferable to provide safety mechanism in the nature of means for elevating the torque shaft and material engaging means for purposes of raising the same from contact with the obstructing matter which is imposing the overload upon the driving mechanism. Various mechanical elevating or raising mechanisms are old in the art but the present mechanism contemplates the use of chicient, simple, and inexpensively operated hydraulically actuated mechanism for elevating the torque shaft and material engaging means, the same being illustrated in detail in Figs. 1, 2, 9, and 14 through 16.

The elevating or raising mechanism illustrated in Figs. 1, 2 and 9 is shown in conjunction with the embodiment of driving mechanism first described above which includes the pushing and pulling type pawl system, while that shown in Figs. 14 through 16 is illustrated in conjunction with the last described embodiment. However, it is to be understood that similar hydraulic elevating mechanisms of the natures illustrated may be employed with the second described embodiment of driving mechanism illustrated herein as well as any other type of hydraulically actuated driving means contemplated within the scope of the present invention. Also, it is to be understood that the embodiments of elevating mechanisms shown and described herein are merely exemplary embodiments since the basic features thereof may be incorporated in other specific forms thereof functioning to produce the desired results of the mechanism illustrated.

In the elevating mechanism shown in Figs. 1, 2 and 9, a plurality of spaced vertical supports 176 are fixed to and supported by the superstructure 14. Horizontal beams 178 are fixed to the upper ends of supports 176 and a plate 180 is secured thereto for purposes of supporting the lower end of a hydraulic cylinder 182. Said cylinder contains a piston and a piston rod 184 projects vertically from the upper end of cylinder 182. A cross-head 186 is adjustably fixed to the upper end of the piston rod 134 and vertical connecting rods 188 extend between and are fixed to the cross-head 186 and a lower cross-head 190. The upper end of the torque shaft 34 projects through the lower cross-head 190 and is connected thereto by any suitable bearing structure which will permit the rotation of the torque shaft 34 relative to the lower cross-head 190. Such bearing means is not shown in detail but is generally designated 192. Obviously, the bearing means 192 should be of a heavy-duty nature so as to permit not only rotation of the torque shaft 34 and the material engaging means 38 relative to the elevating mechanism 18 but said bearing is also of the thrust type and supportsthe means especially when the same is raised above the normal position thereof by the functioning of the elevating mechanism 18 as described hereinafter. Further, the connection between the ratchet wheel 30 and the torque shaft 34 is of such nature that the shaft may be moved vertically relative to the ratchet wheel but non-rotatable relative to the ratchet wheel 30. While such connection is not shown in detail, a conventional sliding key or other type of connection may be used.

Opposite ends of the cylinder 182 are connected to fluid lines 194 and 196. The arrangement of the fluid lines 194 and 196 in Figs. 2 and 9 is slightly different in illustration but the function is identical, the illustration in Fig. 2 being somewhat more diagrammatic than that in Fig. 9. The line 194 is the return line for the fluid pressure and is connected to the pressure return line 68 of the pump 62. The line 196 of the hydraulic cylinder 182 is the pressure line for the elevating cylinder and is connected to one side of an adjustably settable, pressure responsive valve 198. The other side of the valve 198 is connected by a line 200 to the pressure line 66 of the pump 62. Positioned between and connected to the pressure line 196 and the return line 194 of the elevating cylinder is a bleed-back valve 202.

In operation, the elevating mechanism 18 functions as follows. Assume that the material engaging means 38 has encountered an obstruction of any nature such as the unusual settling of solids to such an extent that the movement of the engaging means is either greatly retarted or stopped. Under this condition, the pump 62 which is continuously actuated at a steady speed by the motor 64 will build up pressure in the pressure supply line 66 and said pressure will be interconnected by valve 70 to one end or the other of cylinder 46 for purposes of actuating the ratchet wheel 30. If the impedance of the movement of the engaging means is sufiiciently great or stoppage of the ratchet wheel accurs, the pressure in line 66 will build up to a pre-determined amount for which the pressure actuated valve 198 is set and, when said pie-determined pressure is attained in the line 66 and the line 200 directly connected to valve 198, said valve opens and permits the fluid under said pressure to enter line 196 of the elevating cylinder 182 so as to actuate the piston thereof and thereby raise the torque shaft 34 and material engaging means 38.

Depending upon the setting of the valve degree of pressure required to rotate the torque shaft and material engaging means thereon, the torque shaft and material engaging means may be rotating at a much slower speed than normal or rotation may have substantially ceased at the time such elevation takes place. In any event, the setting of the valve 193 should be such that no damage to any part of the mechanism occurs as a result of the impedance or stoppage of the torque shaft and material engaging means before the valve 198 is actuated to institute operation of the elevating mechanism 18.

After the elevating mechanism 18 has started to function. elevation will continue until the impedance imposed upon the material engaging means 38 has been overcome sufliciently to relieve the pressure built up in the line 66 and, when said pressure has been so relieved that it falls below the pressure setting of valve 198, rotation of the ratchet wheel and the mechanism driven thereby will be resumed at speeds at or approximating normal operating speeds while the torque shaft and material engaging means 38 are substantially at the position to which they were elevated for purposes of overcoming the impedance or obstruction referred to. Such rotation will usually serve to clear the impedance in the lower part of the tank either by moving it toward the outlet port 44 or, if the impedance continues and is sufficiently great, subsequent elevations and rotations of the torque shaft and material engaging means may be necessary before the impedance is completely overcome.

198 and the Following the elevation of the torque shaft by a temporarily abnormal deposit of solids, the abnormal amount thereof will gradually be fed to the outlet 44 and the material engaging means 38 will descend subsequently to its normal operating position. The bleed-back valve 202 will permit hydraulic fluid beneath the piston in cylinder 182 to flow back therefrom, through line 196, into fluid return line 194 and from there to line 68 and the low pressure side of the pump 62. During such operation, the valve 198 is closed and the fluid is therefore by-passed through bleed-back valve 202. The piston of cylinder 182, in returning to its normally lowest position can draw hydraulic fluid from the reservoir of the pump into the upper part of the cylinder 182, the latter then functioning as a reservoir and the pump reservoir need only contain enough fluid at any time to fill the lines of the system and keep the opening on the suction side of the pump immersed at all times.

In the embodiment shown in Figs. 14 through 16, a similar elevating mechanism is incorporated in the operating system for the same purpose as the cylinder 182 in the above described embodiment. However, the cylinder 182 is connected in the hydraulic system of the embodiment of Figs. 14 through 16 in a somewhat different manner. Nevertheless, the mechanical connections of the elevating piston to the drive shaft 34 are the same.

Referring to Figs. 14 through 16, it will be seen that a plurality of adjustable, pressure responsive, relief valves 250 and 252 are respectively connected in the pressure lines 214 and 216. Upon the material engaging means 38 encountering an obstruction or overload as described above in connection with the other embodiment, an excessive amount of pressure will be developed against the driving faces of the pistons in the cylinders 128 and 122 in an effort to continue to drive said material engaging means. in order that no damage will occur in the driving mechanism under these conditions however, the pressure relief valves 250 and 252 are both similarly set to bypass fluid after a predetermined pressure is exceeded in the pressure lines 214 and 216. The fluid by-passcd from the valves 250 and 252 is discharged into a pressure line 254 which is connected at its ends to the relief discharge orifices of said valves. A feed line 256 extends between the pressure line 254 and the lower end of cylinder 182, whereby the by-passed fluid will elevate the piston within the cylinder and thereby raise the drive shaft 34 and material engaging means relative to the tank 18 in order to overcome the obstruction or excessive load encountered by the material engaging means. While such elevating is taking place, a pressure of pre-determined amount in accordance with the setting of relief valves 250 and 252 is maintained upon the drive pawls 204 and 206 so that, upon the material engaging means being elevated to a position where the obstruction is overcome, rotation of the material engaging means will immediately resume. Actually, in many instances, rotation will not be stopped but will merely be slowed to a speed below preferred operating speeds and elevation can take place to overcome the impedance to the material engaging means so that normal operating speeds may be resumed.

The system also includes a by-pass and fluid return line 258- connected between the pressure line 254 and the pump return line 212, the return line 258 having a flow control valve 260 mounted therein, said valve being arranged so that restricted flow is in the direction from line 254 to line 212. Under this arrangement, the flow of fluid from the lower end of cylinder 182 is relatively slow in view of the valve 260 being set for a relatively small opening. During the elevating of the piston in cylinder 182, fluid under pressure is also by-passed through flow control valve 260 from pressure line 254 to return line 212. However, the amount of flow through valve 260 and return line 258 is of such proportion that it does not unduly interfere with the elevating operation of cylinder 182. Further, the valve 260 and the manner in which the cylinder 182' is connected between pressure line 254 and return line 212 is such that when the material engaging means is rotating under normal condit'ons, both ends of thecylinder 182 are full of hydraulic fluid, whereby the cylinder is ready for elevating operation the. instant the pressure in lines 214 and 216 exceeds the setting of relief valves 250 and 252.

The relief valves 250 and 252 are incorporated in the system in such manner as to cooperate and supplement each other regardless of which pawl happens to be driving at the time an obstruction or overload occurs. in order that no return flow will occur between the pressure end of cylinder 182 during elevating movement and the. nondriving cylinder 12b or 122, check valves 262 are mounted in pressure line 25'4 preferably adjacent the pressure relief valves- 2'50 and 252 so as to permit how of fiuid through line I54 only from the valves 250 and 252' to the lower end of cylinder 182. It will thus be seen that the valves 250' and 252 are not only pressure relief valves but, in conjunction. with the check valves 262, they comprise sequence valves as well so as to cause elevation of the piston in cylinder 182 regardless of which relief valve is open. or if both are open.

The instant an obstruction or overload decreases or has been overcome to the point where it is below the pressure setting of the valves 254) and 252, said valves will close the pressure supply to line 254 and fiuid will pass from the lower end of cylinder 182 through line 256 and flow control valve 260, which will restrict the flow of said fluid so as to eiiect a relatively slow decent of the piston and material engaging means. Fluid passing through the valve 260 will be by-Passed by line 264 to the upper end of the cylinder as a result of the weight of the piston therein and the material engaging means, and negative pres are in the upper end of said cylinder will maintain a reservoir of hydraulic fluid in theupper end of the cylinder 182 during normal operation of the material engaging means.

As. is well known in pressure relief valves such. as valves 250 and 252, there will be a small amount of seepage of fluid past the valve seals. In order that such seepage may not accumulate within the valve so as possibly to cause a hydraulic binding or block, an. external drain line 266,, shown diagrammatically in. Fig. 15, is provided to return the seepage to the supply system at atmospheric pressure.

It will therefore be seen that the various embodiments of the present invention contemplate the use of hydraulically operated elevating mechanism for the torque shaft and material. engaging means operable in conjunction with the driving means therefor. The elevating mechanism is rugged and extremely simple, the same being actuated by control mechanism of a relatively inexpensive natureand fool-proof. in operation, whereby even when an abnormal impedance or obstruction of any nature is encountered by the material engaging mechanism, the impedance may either be overcome automatically without stopping the mechanism or, if the impedance is of a very abnormal nature so that the operation of the mechanism is automatically shut off, no injury to any part of the entire mechanism will occur.

While the invention has been shown and illustrated in its several preferred embodiments, and has included certain details, it should be understood that the invention is not to be limited to the precise details herein illustrated and described since the same may be carried. out in other ways falling within the scopeof the invention as claimed.

I claim:

1. A material handling. device including a tank. and a material engaging means therein driven by a shaft subjectedto substantial torque thereby, in combination with hydraulic cylinder and reciprocable piston means, said piston means being reciprocable in opposite directions, a ratchet wheel interconnected to said shaft, arm's each movably interconnected at one' end tosaid piston means and reciprocable thereby, said arms extending axially of said piston and cylinder means substantially tangentially to said ratchet wheel periphery, pawls directly carried by the other ends of said arms, means connected to said arms and operable to urge the pawl carrying ends of said arms toward the teeth of said ratchet wheel, and hydraulic pressure supplying means connected to said cylinder means and hydraulic control means interconnected therebetween, said control means being operable to change the direction of movement of said piston means to cause said arms and pawls to be reciprocated sequentially in driving direction, thereby to eiiect unidirectional rotation of said shaft and material engaging means.

2 A material handling device including a tank and a material engaging means therein driven by a shaft subjected to substantial torque thereby, in combination with hydraulic cylinder and reciprocable piston means, said piston means being reciprocable in opposite directions, a ratchet wheel interconnected to said shaft, arms each movably interconnected at one end to said piston means and reciprocable thereby, said arms extending axiallyof said piston and cylindermeans substantially tangentially to said ratchet wheel periphery, pawls directly carried by the other ends of said arms, means connected to said arms and operable to urge the pawl carrying ends of said arms toward the teeth of said ratchet wheel, hydraulic pressure supplying means connected to said cylinder means and hydraulic control means interconnected therebetween, said control means being, operable to change the direction of movement of said piston means to cause said arms and pawls to be reciprocated sequentially in driving direction, thereby to effect unidirectionai rotation of said shaft and material engaging means, and actuating means carried by said arms and during the reciprocation thereof engaging said control means and operating the same to effect said changing in direction of movement of said arm means and pawls.

3. A material handling device including a tank having material engaging means rotatable therein and driven by a shaft extending into said tank and subjected to high torque by the engagement of material within said tank by said means, in combination with power means, reci'procable means movable in opposite directions thereby, a ratchet wheel interconnected to said shaft of said material handling device, a plurality of arms movably connected at one end to said reciprocable means and reciprocable in driving and non-driving movements thereby, said arms extending axially of said reciprocable means substantially tangentially to the periphery of said ratchet Wheel, a pawl directly connected to the other end of each of said arms, the pawl carrying ends of said arms being disposed adjacent opposite edges to said ratchet wheel and said pawls being operable to engage teeth substantially on'said opposite edges of said ratchet wheel, one of said pawls being shaped and positioned relative to its arm to engage the teeth of said ratchet wheel in pulling relationship and the other being shaped and posit-ioned relative to its arm to engage said teeth in pushing relationship during said driving movements of said arms, whereby upon reciprocation of said arms in one direction one pawl drives the ratchet wheel while the other pawl moves in non-driving direction and vice versa, thereby unidirectionally and substantially continuously rotating said shaft and similarly driving; said material engaging means.

4 A material handling device including a tank having material engaging means rotatable therein and driven by a shaft extending into said tank and subjected to substantial torque thereby, in combination with power means, reciprocable means actuated thereby in opposite directime, a plurality of arms movably connected at one end to said reciprocable means and movable thereby in driving and non-driving directions thereby, a ratchet wheel interconnected to said shaft, a pawl directly connected to the other end of each of said arms, the pawl carrying ends of said arms being disposed-adjacent opposite edges of said ratchet wheel and said pawls being operable to engage teeth substantially on opposite edges of said ratchet wheel during the movement of said pawls by said arms, one of said pawls being shaped and positioned relative to its arm to engage the teeth of the ratchet wheel in pulling relationship and the other pawl being shaped and positioned relative to its arm to engage the teeth of the ratchet wheel in pushing relationship during the driving movements of said arms, whereby as one pawl drives the ratchet wheel the other pawl is moving in non-driving direction and vice versa, one of the inter-engaging faces of each of said pawls and ratchet wheel teeth being cam-shaped, whereby the movement of said pawls into the notches between said teeth also moves said ratchet wheel in driving direction and supplements the driving movement of said reciprocating arms and pawls, thereby substantially continuously rotating said shaft uni-directionally and similarly driving said material engaging means.

5. Mechanism operable to rotate a drive shaft about a vertical axis within the tank of a material handling device and thereby drive material engaging means disposed within said tank, said mechanism comprising in combination, hydraulc power means, reciprocable means actuated thereby in opposite directions, a ratchet wheel interconnected to said shaft, a plurality of pawls interconnected to and operable sequentially by said reciprocating means in driving direction and said pawls alternatively engaging during movement thereof in driving direction said ratchet wheel, thereby substantially continuously to rotate said ratchet wheel and shaft unidirectionally and similarly drive said material engaging means relative to said tank, solenoid actuated valve means interconnected to said hydraulic means and operable to control the operation thereof and said reciprocable means so as to change the direction of movement of said reciprocable means by said hydraulic means and effect said sequential movement of said pawl carrying means in driving direction, switches positioned adjacent the path of movement of and reciprocating means, and actuating means carried by said reciprocating means and operable during movement of said means to engage said switches and actuate said solenoid valve means, thereby to effect predetermined movement of said reciprocating means at the time and in the direction desired to produce said uni-directional rotation of said ratchet wheel and material engaging means.

6. Mechanism operable to rotate the drive shaft of a material handling device including a tank in which said shaft is rotatable about a vertical axis and drives material engaging means disposed within said tank, said mechanism comprising hydraulic power means, reciprocable means actuated thereby in opposite directions, a ratchet wheel interconnected to said shaft, a plurality of arms operable sequentially by said reciprocating means in driving and non-driving directions, a pawl carried by each arm adjacent one end thereof and movable therewith radially of said ratchet wheel and into driving engagement with teeth of said wheel, said driving engagement of said pawls with said ratchet wheel occurring sequentially and alternatively while the pawls are moved by said arms in driving direction, thereby substantially continuously to rotate said ratchet wheel and shaft uni-directionally and similarly drive said material engaging means relative to said tank, valve means interconnected to said hydraulic power means and controlling the operation of said arm by said hydraulic power means so as to change the direction of movement of said reciprocable arms by said hydraulic means and thereby effect said sequential movement of said pawls, and valve actuating means carried by said arms and operable during the movement of said arms to actuate said valve and effect said change in direction'of reciprocation of said arms.

7. Mechanism operable to rotate the drive shaft of a material handling device including a tank in which said shaft is rotatable about a vertical axis to drive material engaging means disposed withing said tank, said mechanism comprising a hydraulic cylinder, a piston and rod reciprocable thereby in opposite directions, a ratchet wheel interconnected to said shaft, a plurality of arms movably connected at one end to said piston rod and reciprocable thereby in driving and non-driving directions, a pawl directly carried by the other end of each arm, said pawls engaging opposite sides of said wheel, means normally urging said pawls into engagement with the notches between the teeth of said wheel, one of said pawls being arranged to engage the teeth of said ratchet wheel in pulling relationship when the piston rod moves in one direction and the other in pushing relationship when the piston rod moves in the opposite direction, whereby as one pawl moves in driving direction to rotate said ratchet wheel the other pawl moves in non-driving direction and said pawls during the reciprocation of said piston rod alternately and sequentially engage said ratchet wheel while said pawls move in driving direction and cooperate substantially continuously to rotate said ratchet wheel and shaft uni-directionally and similarly drive said material engaging means relative to said tank, valve means operable to control the operation of said hydraulic means and piston rod, and valve actuating means carried by said pawl carrying arms and operable at the end of each reciprocation thereof to actuate said valve means and thereby change the direction of movement of said piston rod by said hydraulic cylinder.

8. Mechanism operable to rotate the drive shaft of a material handling device including a tank in which said shaft is rotatable about a vertical axis to drive material enagging means disposed within said tank, said mechanism comprising a plurality of hydraulic cylinders, a piston and rod reciprocable in opposite directions by each piston, a ratchet wheel interconnected to said shaft, an arm pivotally connected at one end to each piston rod and reciprocable longitudinally thereby in driving and non-driving directions, said arms extending substantially axially of said piston rods and each having a pawl directly connected to the other end thereof and said ends and pawls being movable toward said ratchet wheel in a direction substantially radial thereto and arranged to engage the teeth of said wheel at positions spaced circumferentially on said wheel, valve means operable to control the operation of said hydraulic cylinders and pistons and cause said pistons to move sequentially in driving direction, one of said pawls moving in driving direction while the other pawl is moving in non-driving direction and vice versa, whereby said pawls cooperatively drive said wheel substantially constantly and uni-directionally, said ratchet wheel thereby similarly driving said shaft and material engaging means.

9. Mechanism operable to rotate a drive shaft about a vertical axis within the tank of a material handling device and thereby drive material engaging means disposed Within said tank, said mechanism comprising a plurality of hydraulic cylinders, a piston and rod reciprocable by each piston, a ratchet wheel interconnected to said shaft, a plurality of arms pivotally connected at one end of each to said piston rods and respectively reciprocable longitudinally by said rods in driving and non-driving directions, said arms extending substantially axially of said cylinder and piston rod means, pawls carried by the opposite ends of said arms and respectively engaging the teeth of said wheel at circumferentially spaced positions. means operable resiliently to urge said pawls into notches between said teeth, valve means operable to control the operation of said hydraulic cylinders and pistons and integrate such operation to move said pistons sequentially in driving direction, means arranged to actuate said valve means to effect the reversal of each of said pawls from non-driving to driving direction before the other pawl has started its movement in non-driving direction and thereby partially overlap the driving movements of the pawls and permit the variation in driving pressures be tween the start of the driving cycle and full load conditions to cause the pawl starting its driving stroke to move more rapidly than and catch up with the pawl under full driving load before the latter completes its driving stroke, whereby said pawls cooperate to rotate said wheel constantly and unidirectionally.

l0. Mechanism operable to rotate the drive shaft of a material handling device including a tank in which said shaft is rotatable about a vertical axis and drives material engaging means disposed within said tank, said mechanism comprising a plurality of hydraulic cylinders, a piston and rod reciprocable in opposite directions by each piston, a ratchet wheel interconnected to said shaft, an arm connected at one end to each piston rod and extending substantially axially therefor for reciprocation thereby in driving and non-driving directions, a pawl directly connected to the other end of each arm and said pawls being similar and engageable with the teeth of said wheel at circumferentially spaced positions, means normally urging said pawls into engagement with the notches between the teeth of said wheel, a solenoid actuated valve operable to control the operation of each hydraulic cylinder and piston, apairof spaced switches positioned adjacent the path of movement of each pawl carrying arm, a circuit connecting said switches with the solenoid valve controlling the movement of each arm, said switches when actuated respectively shifting the valves to reverse the direction of movement of said arms, means on said arms engageable during the movement thereof with said switches to actuate said valves, said switch engaging means and valves being positioned and synchronized to actuate said pistons and pawls sequentially in driving direction, one of said pistons and the pawl actuated thereby moving in driving direction while the other piston and pawl is moved in non-driving direction and vice versa, whereby said pawls successively move in driving direction and sequentially engage said ratchet wheel cooperatively to rotate said wheel substantially constantly and uni-directionally, said ratchet wheelsimilarly rotating said shaft and material engaging means.

11. Mechanism operable to rotate the drive shaft of a material handling device including a tank in which said shaft is rotatable about a vertical axis and drives material engaging means disposed within said tank, said mechanism comprising a hydraulic cylinder, a piston and rod reciprocable thereby in opposite directions, a ratchet wheel interconnected to said shaft and having two integrated series of differently shaped teeth individually arranged in alternate relationship around the periphery of said wheel, the teeth of each series being similar, a plurality of pawl carrying arms connected tosaid' piston rod and reciprocable thereby in driving and non-driving directions for a distance equal at least to the circumferential length of one tooth, said pawls being engageable with the teeth at opposite edges of said wheel, rneansnorm-ally urging saidpawls intothe notches between the teeth of said wheel, one of said pawls being arranged to engage the teeth of one series of said ratchet wheel in pulling relationship when the piston rod moves in one direction and the other pawl engaging the teeth of the other series in pushing relationship when the piston rod moves: in the other direction, whereby as one pawl moves in driving direction a distance equal to the length of one tooth to rotate said ratchet wheel the other pawl moves in" nondriving direction a similar distance but relative to two teeth due to the movement of the wheel, said pawls during the reciprocation of said piston rods alternately and sequentially engaging said ratchet wheel and cooperating substantially continuously to rotate it and said shaft uni directionally and similarly drive said material engaging means relative to said tank, and valve means operable to control the operation of said hydraulic means and piston rod and actuatable at the end of each reciprocation of said piston rod to reverse the direction of movement of said piston rod by said hydraulic cylinder.

l2. Mechanism operable to rotate the drive shaft of a material handling device including a tank in which said shaft is rotatable about a vertical axis and drives material engaging means disposed within said tank, said mechanism comprising a hydraulic cylinder, a piston and rod reciprocable thereby in opposite directions, a ratchet wheel interconnected to said shaft and having two integrated series of differently shaped teeth individually arranged in alternate relationship around the periphery of said wheel, the individual teeth of each series being similar, a plurality of pawl carrying arms connected to said piston rod and reciprocable thereby in driving and non-driving directions for a distance equal at: least to the circumferential length of one tooth, said pawls being engageable with the teeth at opposite edges of said wheel, resilient means urging said pawls into the notches between the teeth of. said wheel, one of said pawls being arranged to engage the teeth of one series of said ratchet wheel in pulling relationship when the piston rod moves in one direction and the other pawl engaging the teeth of the other series in pushing relationship when the piston rod moves in the opposite direction, whereby as one pawl moves in driving direction a distance equal to the length of one tooth to rotate said ratchet wheel the other pawl moves in non-driving direction a similar distance but relative to two teeth due to the movement of the wheel, said pawls during the reciprocation of said piston rods alternately and sequentially engaging said ratchet wheel and cooperating substantially continuously to rotate it and said shaft uni-directionally and similarly drive said material engaging means relative to said tank, means carried by said ratchet wheel and operable during the rotation thereof to prevent the pawls while moving in non-driving direction from moving into the intervening tooth notches between those of the respective teeth of the series respectively engaged by said pawls when moving in drivingdirection, and valve means operable to control the operation of said hydraulic means and pistonrod and actuatable at the end of each reciprocation of saidpiston rod to reverse the direction of movement of said. piston rod by said hydraulic cylinder.

13'. Mechanism operable to rotate the drive shaft of a material handling device including a tank in which said shaft is rotatable about a vertical axis and drives material engagingmeans disposed within said tank, said mechanism comprising a hydraulic cylinder, a piston and rod reciprocable thereby in opposite directions, a ratchet wheel interconnected to said shaft, a plurality of pawl carrying arms connected to said piston rod and reciprocable thereby in driving and non-driving directions, said pawls respectively engaging teeth on opposite edges of said wheel, means normally urging said pawls radially into engagement with the notches between the teeth of said wheel, one of said pawls being arranged to engage the teeth of said ratchet wheel in pulling relationship when the piston rod moves in one direction and the other in pushing relationship when the piston rod moves in the opposite direction thereof, whereby as one pawl moves in driving direction to rotatesaid ratchet wheel the other pawl moves in non-driving direction and said pawls during, the movement thereof in driving direction alternately and sequentially engage said ratchet wheel and thereby cooperate substantially continuously to rotate said ratchet wheel and shaft uni-directionally and similarly drive said material engaging means relative to said tank, and valve means operable to control the operation of said hydraulic means and piston rod and actuatable at the end of each reciprocation of' said piston rod to reverse the direction of movement of said piston rod by said hydraulic cylinder, the faces of the' ratchet wheel teeth engaged by the pawls for driving said wheel being angularly inclined to the radius of the wheel to provide cam surfaces which when said pawls are moved by said urging means into the -23 notches between the teeth of the wheel coact with said pawls in camming relationship and thereby move said wheel in its direction of rotation and overcome any momentary interruption of such rotation during the reversal in reciprocation of the piston rod.

14. A material handling device including a tank and material engaging means therein rotatably driven by a shaft, in combination with means rotatably to drive said shaft comprising a ratchet wheel interconnected to said shaft, a plurality of hydraulic cylinders having pistons reciprocable therein, a pair of pawls engageable with the teeth of said ratchet wheel at circumferentially spaced positions on said wheel, said pawls respectively being interconnected to said pistons and movable in driving and non-driving directions thereby, a hydraulic pump, pressure lines interconnecting said pump to said cylinders, an adjustable flow control valve in each line, and control means also connected in said lines and operable to direct fluid under pressure alternately to the driving ends of said cylinders, said flow control valves being regulatable to cause said pistons to actuate said pawls with desired force and sequentially in driving engagement with said ratchet wheel and thereby rotate the same unidirectionally and continuously.

15. A material handling device including a tank and material engaging means therein rotatably driven by a shaft, in combination with means rotatably to drive said shaft comprising a ratchet wheel interconnected to said shaft, a plurality of hydraulic cylinders having pistons reciprocable therein in opposite directions, a pair of pawls respectively interconnected to said pistons and engageable with the teeth of said ratchet wheel at circumferentially spaced positions on said wheel, said pawls respectively being movable in driving and non-driving directions by said pistons, a hydraulic pump, pressure lines interconnecting the inlet and outlet ends of said pump to the opposite ends of said cylinders, an adjustable flow control valve in each line, the valves in the lines to the nondriving end of the cylinders being set to permit greater flow of hydraulic fluid to said ends than to the driving ends thereof, thereby to cause faster movement of the pawls in non-driving than driving direction, valve control means connected in said pressure lines and operable to direct fluid under pressure alternately to the driving ends of said cylinders, and means operable in response to the movement of said pawls to shift said valve control means so as to cause one pawl to start driving movement before the other pawl has completed driving movement, whereby the driving strokes of said pawls partially overlap and operate to rotate said ratchet wheel unir directionally and continuously.

l6. A material handling device including a tank and material engaging means therein rotatably driven by a shaft, in combination with means rotatably to drive said shaft comprising a ratchet wheel interconnected to said shaft, a plurality of hydraulic cylinders having pistons reciprocable therein and disposed on opposite sides of said shaft, a pair of pawls respectively interconnected to said pistons and engageable with the teeth of said ratchet wheel at substantially diametrically opposed edges of said wheel, said pawls respectively being movable in driving and non-driving directions by said pistons substantially axially thereof, a hydraulic pump, pressure lines interconnecting said pump to said cylinders, and control valve means connected in said pressure lines and operable to direct fluid under pressure alternately to the driving ends of said cylinders, whereby said pistons actuate said pawls sequentially in driving engagement with said ratchet wheel and rotate the same uni-directionally.

17. A material handling device including a tank and F material engaging means therein rotatably driven by a shaft, in combination with means rotatably to drive said shaft comprising a ratchet wheel interconnected to said shaft, a plurality of hydraulic cylinders disposed on opposite sides of said shaft and having pistons reciprocable therein, a pair of pawls respectively interconnected to said pistons and engageable with the teeth of said ratchet wheel at substantially diametrically opposed edges of said wheel, said pawls respectively being movable in driving and non-driving directions by said pistons substantially axially thereof, a hydraulic pump, pressure lines interconnecting said pump to said cylinders, control valve means connected in said lines and operable to direct fluid under pressure alternately to the driving ends of said cylinders, and means operable in response to the movement of said pawls to shift said control valve means so as to cause one pawl to start driving movement before the other pawl has completed driving movement, thereby affording partial overlapping of the pawl driving movements and rotating said ratchet wheel uni-directionally and continuously.

18. A material handling device including a tank and material engaging means therein rotatably driven by a shaft, in combination with means rotatably to drive said shaft comprising a ratchet wheel interconnected to said shaft, a plurality of hydraulic cylinders disposed on opposite sides of said shaft and having pistons reciprocable therein, a pair of pawls respectively interconnected to said pistons and engageable with the teeth of said ratchet wheel at substantially diametrically opposed edges of said wheel, said pawls respectively being movable in driving and nondriving directions by said pistons substantially axially thereof, a hydraulic pump, pressure lines interconnecting said pump to said cylinders, and control means operable in response to the movement of said pawls to direct fluid under pressure alternately to the driving ends of said cylinders and positioned relative to the movement of said pawls to effect reversal of movement of said pawls after the same have moved in non-driving direction a distance to engage only alternate teeth of the ratchet wheel, one of said pawls engaging only the teeth intervening those engaged by the other pawl, whereby said pistons actuate said pawls sequentially in driving engagement with said ratchet wheel and thereby rotate the same uni-directionally.

19. A material handling device including a tank having a vertical shaft, means mounting said shaft for vertical and rotary movements and material engaging means within said tank driven by said shaft, in combination with hydraulic pressure means, hydraulically actuated driving means connected to said hydraulic pressure means and operable thereby to rotate said shaft, hydraulically 'ac'tuated elevating means interconnected to said shaft and arranged to be operated by said hydraulic pressure means, and a pressure responsive valve hydraulically connected between said ele ating means and said pressure means and operable at a set pressure in excess of those normally required to rotate said shaft, said valve being operable to divert hydraulic fluid from said pressure means to said elevating means and thereby raise said shaft and material engaging means within said tank upon said material engaging means encountering an overload imposing upon said driving means a resistance force exceeding said set pressure.

20. A material handling device including a tank having a vertical shaft, means mounting said shaft for vertical and rotary movements and material engaging means within said tank driven by said shaft, in combination with a hydraulic pump, hydraulically actuated driving means, a supply line connecting said driving means to the pressure side of said pump, said driving means being operable thereby to rotate said shaft, hydraulically actuated elevating means interconnected to said shaft and operable by fluid from said pump, a pressure and responsive valve hydraulically interconnected between said elevating means and the pressure side of said pump and operable at a set pressure in excess of those normally required to rotate said shaft, said valve being operable to divert fluid from said pump to said elevating means and thereby raise said shaft and material engaging means within said tank and 

